The possible contribution of glial cell potentials to the electroretinogram will be investigated. Retinas of carp and clawed toad (Xenopus) will be studied. As a working hypothesis it is supposed that voltage changes across the glial cell membrane are initiated by light induced alterations in potassium efflux from retinal neurons. The sinks and sources of neural activity in the retina will be estimated through analysis of the radial distribution of currents associated with particular light evoked waveforms. Related changes in potassium ion concentration will be measured with K specific electrodes. Certain pharmacological agents will be applied to simplify the photovoltages recorded. A second project seeks to relate synaptogenesis in the outer plexiform layer (OPL) of the retina to the appearance of electroretinogram components. Normal development in Xenopus will be the baseline against which alterations in synapse formation induced by dietary deprivation of Vitamin A and/or fatty acids will be measured. The synaptogenic sequence of the OPL will also be studied in cultured eye rudiments of the frog, Rana pipiens.